1. Field of the Invention
The present invention relates generally to bar code scanning systems, and in particular to a method and apparatus for optimizing or at least improving the relative positions of bar code scanner and symbol to be read, during data acquisition.
2. Description of the Prior Art
A frequently encountered problem with bar code scanning, is the difficulty of aligning the scanner in a manner which allows optimal code word (data character) acquisition from the symbol. This may be especially true of two-dimensional bar code symbols having a very low height to width ratio. The best acquisition occurs when the scan line is parallel to the symbol, and crosses none of the rows of the symbol. In certain currently-available bar code scanners, acquisition can still be carried out at up to several degrees of parallel, but at a processing, and consequently at a speed, cost. If the scan line is too skew with respect to the symbol, then the symbol cannot be decoded at all. Decoding may also be difficult if the symbol is slightly skew with respect to the scan line, and is also a relatively long way away from the scanner.
Previous methods of improving the readability of bar code symbols have concentrated upon maintaining the printed quality of the symbol itself, and ensuring that the printed symbol can easily be read under optimal conditions. To that end, there have been several proposals for devices which check printed symbol quality, such as the relative width of the bars and spaces, to provide a warning to the printer if the bar code quality degenerates to such an extent that difficulties are likely to be experienced when the symbols ultimately come to be read (for example in a supermarket environment). One such method for checking the quality of printed bar code symbols is disclosed in U.S. Pat. No. 4,251,798, commonly assigned with the present application. Further details of a bar code verification device which was sold by the present assignee under the brand name "Laserchek.RTM." may be found in the article by J. Swartz of May 1, 1980, entitled "Percent Decode, POS Scanability, and the Laserchek Symbol Analyzer" published by Symbol Technologies, Inc.
The intention of all of these prior art systems was to reduce the number of misreads by end users (for example, supermarket checkout staff) to as low a value as possible by maintaining rigorous quality control on the printed symbol itself. Clearly, the higher the quality of the printed symbol, the more leeway there will be for a checkout operator to miss a line or otherwise mis-align or otherwise poorly position the bar code reader with respect to the symbol being read without a misread resulting.